Nozzle for producing fluid cutting jet

ABSTRACT

A nozzle for producing high pressure liquid coherent jets for fluid jet cutting is described, the nozzle being constructed of a corundum crystal having an orifice formed therein of a specific disclosed geometry in which a convergent entrance section merges into a straight-sided exit section, and in which the relationship of the angle of convergency and the length and diameter of the exit section is such that an extension of the convergent side will not intersect the exit section wall, and with the length of the exit section being equal to or greater than its diameter.

United States Patent Chadwick et al.

Sept. 4, 1973 NOZZLE FOR PRODUCING FLUID CUTTING JET Inventors: Ray F. Chadwick Troy; Michael C.

Kurko, Farmington; Joseph A. Corriveau, Southfield, all of Mich.

Assignee: The Bendix Corporation, Southfield,

Mich.

Filed: Mar. 1, 1971 Appl. No.: 119,758

US. Cl. 83/177, 239/601 Int. Cl B26f 3/00 Field of Search 83/53, 177; 239/601,

References Cited UNITED STATES PATENTS 5/1963 Spies Jr 239/601 X 7/1935 Klotzman 239/493 3,532,014 10/1970 Franz 83/53 Primary ExaminerAndrew R. Juhasz Assistant Examiner-Leon Gilden Attorney-John R. Benefiel and Flame, Hartz, Smith & Thompson [57] ABSTRACT 7 Claims, 3 Drawing Figures Patented Sept. 4,1973 3,756,106

FIG. I

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mvsm'ons MICHAEL c. KURKO 56 EP H AQEQRMQIEAU ATTORNEY 1 NOZZLE FOR PRODUCING FLUID CUTTING JET BACKGROUND OF THE INVENTION 1. Field of the Invention This invention concerns fluid jet cutting and more specifically nozzles for fluid jet cutting.

2. Description of the Prior Art The use of high pressure small diameter fluid jets to cut materials such as fabrics, wood, metals, etc., and for such applications as deburring of parts has been proposed, as described in US. Pat. Nos. 2,985,050; 3,212,378; and 3,526,162 and its effectiveness also experimentally demonstrated. This approach offers several attractive advantages over conventional industrial cutting processes such as ease of automating with resulting potential productivity gains, reduced kerf losses, single point cutting, high cutting speeds and other advantages.

However, these systems must efficiently convert a liquid, usually water with or without abrasive or other additives at extremely high pressures, ranging from 15,000 psi to 100,000 psi (with higher pressures limited only by the pumping equipment) into a fluid jet in order to provide the cutting function. Furthermore, this fluid jet must be of relatively small diameter, on the order of 0.002 to 0.025 inches, in order to reduce pumping loads and to produce the very narrow and fine cut desired, and also must be coherent, that is, fan out must be eliminated to the maximum extent possible to effectively concentrate the energy in the jet and produce this fine cut, and to minimize power requirements.

In addition, to be suitable for industrial application, this system must be capable of operating continuously over periods of relatively long duration without excessive maintenance.

These requirements have heretofore prevented practical industrial application of such a fluid jet cutting system inasmuch as, among other difficulties, nozzles have not been produced which will provide such a coherent jet over periods of practical duration at an acceptable cost.

The prior art nozzles used in other related fluid jet applications such as in placer mining operations have not been suitable since in these applications: (a) the fluid jet is operated either at much lower pressures or intermittently; (b) the flow rates and consequently nozzle diameters are much larger and fluid velocities lower, greatly reducing erosion rates and the untoward effects of improper geometry due to erosion or manufacturing errors on jet coherency; (c) most importantly, this application does not require a coherent jet, as a fine kerf is of little or no importance.

In fact, in no other applications is there found the needed combined requirements of critical nozzle geometry which is maintainable at extreme pressures and over long periods, and produceable at a reasonably low cost. Thus, prior art efforts turned to many varying nozzle geometries and materials such as tool'steel, sintered ceramics, plastics and diamond. All except diamond are quickly eroded to the extent that jet coherence is lost due to disfigurement of the nozzle geometry and/or pressure decays due to nozzle enlargement. The use of diamond has been considered impractical due to high material and machining costs and suitable nozzles geometries are difficult to machine.

Sintered aluminum oxide and tungsten carbide have also been tried without success due to difficulties in obtaining required surface finishes which are also necessary to insure efficiency, coherency, and minimum erosion rates. These materials also did not meet the erosion requirements due to failure of the bond holding the particles together.

Similarly, the requirements of small orifice size, jet coherency, low fabrication costs, close tolerances on the nozzle configuration, fine surface finishes, and the need to use a very hard, strong material to combat erosion has led to great difficulties in arriving at an acceptable nozzle geometry. Most such configurations which would produce a coherent jet under these flow conditions involved either curved sections or long, very gradually tapering sections, both of which are not feasible to machine on a production basis out of the required very hard and strong nozzle materials.

Therefore, it is an object of the present invention to provide a nozzle for producing a fluid cutting jet in which the nozzle efficiently produces a coherent fluid jet at pressures from 15,000 psi to over 100,000 psi and is operable continuously over a relatively long period of time, yet is inexpensive to produce.

SUMMARY OF THE INVENTION These objects and others which will become apparent upon a reading of the following specifications and claims are accomplished by providing a nozzle which is constructed from a crystal of corundum (sapphire or ruby), and which has a geometry consisting of a straight-sided conical entrance section merging into a straight-sided cylindrical exit section, the degree of convergency of the entrance section and the exit section diameter and length being such that any extension of the convergent side will not intersect an exit section wall, and in which the length of the exit section is equal or greater than the diameter thereof.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic representation ofa fluid jet cutting system according to the present invention.

FIG. 2 is a detailed sectional view of the nozzle assembly depicted schematically in FIG. 1.

FIG. 3 is a detailed representation of the nozzle geometry according to the present invention.

DETAILED DESCRIPTION In the following detailed description, specific embodiments will be described and certain terminology will be employed for the sake of clarity, but it is to be understood that these are merely illustrative and the invention may be practiced in a variety of forms and embodiments.

Referring to the drawing and particularly FIG. 1, a fluid jet cutting system 10 is depicted in schematic form. This system includes a source 12 ofa liquid, preferably water, under pressure. The source is connected to a high pressure intensifier 14 in order to raise the pressure of the liquid to the high pressures required for material cutting. This ranges from a minimum of 15,000 psi to over 100,000 psi, with the most useful pressures being those in excess of 30,000 psi.

Presently, the most effective method of obtaining such pressures in excess of 30,000 psi has been double acting ram type intensifiers as typified by the intensifier described in the US. Pat. No. 2,592,940 which are commercially available.

Liquid under pressures up to 30,000 psi can be contin uously supplied by commercially available high pressure pumps.

The liquid under these high pressures is then transmitted to a nozzle assembly 16 via conduit 15 which creates the high pressure jet 18 that does the actual cutting of a workpiece 20 positioned to be cut by the jet.

After passing through the workpiece, the spent jet may be collected in the collector 22 positioned underneath the workpiece.

Referring to FIG. 2, the nozzle assembly 16 is shown in partial section in some detail. The assembly includes a nozzle orifice 24, pressed into a counter bore 26 in a brass insert 28. This insert is positioned on the end of conduit 15 by means of an end cap 30 threaded to the CD. of the conduit 15, and which serves to seal the insert 28 to the conduit 15 by deformation of the metal. Alternatively, high pressure seals could at this point be used for this purpose.

The nozzle orifice 24 which comprises the improve ment of the present invention is constructed of a single corundum crystal (AL- 0 such as sapphire or ruby. It has been found that this material fulfills all of the described requirements. lt is low in cost since synthetic forms are available commercially, and as such crystals formed with a central aperture have been used commercially for wire drawing dies and lower pressure precision orifices, they are available in high volume production quantities at relatively low cost with or without central apertures formed therein.

Corundum is relatively machinable as compared to diamond since it can be abraded by diamond or aluminum oxide coated or tipped tools to thus allow a variety of shapes to be formed therein and also can be lapped to a very smooth surface finish.

Most importantly, this material has proved to be very resistant to erosion by the high pressure jet, such orifices having been found to last many hours at pressures from 50,000 to 80,000 psi.

Referring to FIG. 3, the details of the nozzle orifice 24 geometry are disclosed. This geometry includes a convergent conical entrance section 32, the straight sides of which form an included angle 6. This section 32 merges into a straight-sided cylindrical exit section 34 of diameter D and lengh L. This geometry is selected so that an extension of the sides of the convergent section 32 will not intersect the wall of the exit section 34. Thus, this extension will either be just tangent to the point A or pass somewhere through the exit diameter of the exit section 34.

Expressed mathematically:

L D/Tan (6/2) in addition, the ratio L/D is equal to or greater than 1.

It has been found that this configuration creates a coherent liquid jet at the pressure described and in the range of diameters D formed to produce suitable cutting jets without the need for curving or long, shallowly tapering core sections. In connection with this, cone angles 9 will usually be greater than 30 thus minimizing machining costs. These diameters D range from approximately 0.002 inches to 0.020 inches, with 0.008 inches being typical.

In a typical design, the nozzle orifice was constructed from a sapphire rod 0.0887 inches in diameter with 0 60, L 0.012 inches and D 0.008 inches. Nozzle cross sections perpendicular to the flow axis were held symmetrical and concentric to within 0.0005 inches, all internal surfaces being highly polished.

It is not known why this particular shape has produced this result inasmuch as neither analytical nor experimental techniques for analyzing this phenomenon have been developed which could verify the reason a coherent jet is produced by this geometry and under these conditions.

As noted, this geometry also fulfills another requirement, i.e., it is relatively easy to machine as it does not involve either curved walls or the long, shallowly tapered shapes common in the prior art.

Thus, commercially available orifices having a shape roughly corresponding to that shown can be successfully lapped smooth and into the precise shape disclosed by the use of equipment and techniques known in lapping drawing dies. In connection with this, it should be noted that in so lapping it is preferable that the shoulder 36 be rounded somewhat to eliminate a sharp change in section.

While a specific embodiment has been described, it can be readily appreciated that the invention is not so limited, and may be practiced in a variety of forms and embodiments.

What is claimed is:

1. An arrangement for producing a fluid cutting jet comprising:

' a nozzle member composed of a corundum crystal having an orifice formed therein, wherein said orifice has a conical entrance section communicating with a cylindrical exit section, and wherein the angle of said conical entrance section and the length and diameter of said exit section being such that an extension of said entrance section walls would not intersect said exit section walls, and wherein said length of said exit section is greater than the diameter of said exit sections;

means for directing liquid under 15,000 pounds per square inch or higher through said orifice formed in said corundum crystal, whereby a very high pressure jet is formed by said liquid issuing through said orifice.

2. The arrangement ofclaim 1 wherein said exit section length is equal to or greater than said diameter of said exit section.

3. The arrangement of claim 1 wherein the included 5 angle of said convergency of said entrance section is 30 or greater.

4. The arrangement of claim 1 wherein the included angle 0 of said conical entrance section, the length L and diameter D of said exit section are related such that:

L D/Tan (0/2) L D/tan (6/2) and L/D s 1 and means for directing a liquid under 15,000 psi or greater through said nozzle member, whereby a coherent high pressure liquid jet is formed. 6. The arrangement of claim 5 wherein said angle 6 is greater than 30.

7. The arrangement of claim 5 wherein said nozzle orifice is composed of a corundum crystal.

I! k =1! i 4 

1. An arrangement for producing a fluid cutting jet comprising: a nozzle member composed of a corundum crystal having an orifice formed therein, wherein said orifice has a conical entrance section communicating with a cylindrical exit section, and wherein the angle of said conical entrance section and the length and diameter of said exit section being such that an extension of said entrance section walls would not intersect said exit section walls, and wherein said length of said exit section is greater than the diameter of said exit sections; means for directing liquid under 15,000 pounds per square inch or higher through said orifice formed in said corundum crystal, whereby a very high pressure jet is formed by said liquid issuing through said orifice.
 2. The arrangement of claim 1 wherein said exit section length is equal to or greater than said diameter of said exit section.
 3. The arrangement of claim 1 wherein the included angle of said convergency of said entrance section is 30* or greater.
 4. The arrangement of claim 1 wherein the included angle theta of said conical entrance section, the length L and diameter D of said exit section are related such that: L < or = D/Tan ( theta /2)
 5. An arrangement for producing a coherent high pressure liquid jet comprising: a nozzle orifice member formed of a corundum crystal and having an orifice formed therein having a conical entrance section and a cylindrical exit section, the included angle theta , and the length L and diameter D of said exit section being related such that: L < or = D/tan ( theta /2) and L/D < or = 1 and means for directing a liquid under 15,000 psi or greater through said nozzle member, whereby a coherent high pressure liquid jet is formed.
 6. The arrangement of claim 5 wherein said angle theta is greater than 30*.
 7. The arrangement of claim 5 wherein said nozzle orifice is composed of a corundum crystal. 